阳山金矿床锶铅同位素组成特征与成矿物质来源

Sr and Pb isotopic feature and ore-forming material source of the Yangshan gold deposit

甘肃阳山金矿位于西秦岭造山带的陕甘川"金三角"地区,是我国最大的卡林型-类卡林型金矿床。本文研究了该矿床赋矿地层、岩浆岩、矿石以及碧口地体碧口群岩石的锶和铅同位素组成特征,获得成矿时的矿石硫化物、赋矿地层三河口群、中生代花岗斑岩、前寒武纪碧口群的锶同位素初始比值(I_(Sr))范围分别是0.70798～0.71697,0.71382～0.72005,0.70918～0.71168,0.70344～0.71009。这些结果表明,初始成矿流体I_(Sr)值应低于赋矿地层、中生代花岗岩,可能主要由碧口地体变质脱水形成。成矿流体在上升过程中与高I_(Sr)值的赋矿地层三河口群发生水岩作用,流体I_(Sr)值增高;高I_(Sr)值的成矿流体与赋矿花岗斑岩脉再次发生水岩作用时,导致部分硫化物I_(Sr)值高于花岗斑岩I_(Sr)值。矿石硫化物^(206)Pb/^(204)Pb、^(207)Pb/^(204)Pb和^(208)Pb/^(204)Pb比值分别为17.552～18.759、15.576～15.928和37.894～39.293,变化范围大于赋矿地层三河口群和花岗斑岩,而与碧口群基本一致,反映了硫化物铅同位素组成主要继承了碧口群的特征,同样指示部分成矿物质来自碧口群。总之,碧口群是不可缺少的成矿流体和物质的来源之一,含碧口群的碧口地体在中生代沿勉略缝合带向北陆内俯冲到阳山矿田之下,在阳山矿田之下发生变质脱水作用,流体上升为成矿系统提供流体、成矿元素和热量。

The Yangshan gold deposit,located in the western Qinling Orogen,is the largest Carlin-like or Carlin gold deposit in China.Given that the ores resulted from interaction between host-rocks and ore-fluids,this paper reports Sr and Pb isotopic composition of ore-hosting strata,magmatites and ores as well as the Bikou Group of the Bikou terrane to constrain sources of ore-forming material and fluid.I_(Sr) ratios of sulfides,ore-hosting Sanhekou Group,Mesozoic granite porphyry and the Bikou Group are 0.70798～0.7...